System to compensate for roll eccentricity effects and/or to simulate a mill with variable stretch characteristics

ABSTRACT

A rolling mill control system which, in one aspect, compensates for the effects of roll eccentricity during operation of the rolling mill. The control system includes circuitry which produces a control signal for rapid and accurate adjustments to hydraulic roll force actuators in a manner to prevent increases in the roll separating force. This circuitry further includes an outer gage control loop and/or tension control loop for automatic gage control of the rolling mill. According to another aspect of the disclosure, the control system simulates a rolling mill structure having variable spring constants whereby an operator may select a desired mode of rolling mill control. To simulate an infinitely stiff mill construction, the control system provides a control signal for rapid adjustments of the roll force actuators in a direction and by the exact amount to compensate for changes in the housing stretch. The control system simulates infinitely soft mill construction by rapid adjustments to the roll force actuator in a direction and by the exact amount to resist changes in the rolling force.

United States Patent [191 Silva Feb. 26, 1974 SYSTEM TO COMPENSATE FORROLL ECCENTRICITY EFFECTS AND/0R T0 SIMULATE A MILL WITH VARIABLESTRETCH CHARACTERISTICS [76] Inventor: Antonio V. Silva, c/oWestinghouse Electric S.A. Caixe Postal 5156, San Paulo, Brazil [22]Filed: Dec. 4, 1972 [21] Appl. No.: 312,178

[52] US. Cl. 72/11 [51] Int. Cl ..B21b 37/12 [58] Field of Search 72/8-ll, 16, 21, 72/ I9 [56] References Cited UNITED STATES PATENTS 3,478,55III/l969 Alsop 72/8 3,543,549 12/1970 Howard 72/8 Primary ExaminerMiltonS. Mehr Attorney, Agent, or FirmR. G. Brodahl [57] ABSTRACT A rollingmill control system which, in one aspect, compensates for the effects ofroll eccentricity during operation of the rolling mill. The controlsystem includes circuitry which produces a control signal for rapid andaccurate adjustments to hydraulic roll force actuators in a manner toprevent increases in the roll separating force. This circuitry furtherincludes an outer gage control loop and/or tension control loop forautomatic gage control of the rolling mill. According to another aspectof the disclosure, the control system simulates a rolling mill structurehaving variable spring constants whereby an operator may select adesired mode of rolling mill control. To simulate an inf nitely stiffmill construction, the control system provides a control signal forrapid adjustments of the roll force actuators in a direction and by theexact amount to compensate for changes in the housing stretch. Thecontrol system simulates infinitely soft mill construction by rapidadjustments to the roll force actuator in a direction and by the exactamount to resist changes in the rolling force.

16 Claims, 2 Drawing Figures GAUGE CONTROL SWITCH TENSION CONTROLLERHOUSING STRETCH MODULATOR INVERTER I 1 39 ACTUATOR POSITION CONTROLLER4| 4o SERVO VALVE SYSTEM TO COMPENSATE FOR ROLL ECCENTRICITY EFFECTSAND/OR TO SIMULATE A MILL WITH VARIABLE STRETCH CHARACTERISTICSBACKGROUND OF THE INVENTION The eccentricity characteristics of rollsemployed in a rolling mill have the detrimental effect of producingcyclic gage errors during the rolling of metallic strip or the like, asa function of the phase relation between the eccentricities of therotating rolls. Conventional rolling mill control systems are based onthe assumption that absolute concentric rolls are provided in the mill;while in actual practice they are too expensive to produce or impossibleto machine and therefore some degree of roll eccentricity is normallypresent. Moreover, the effect of roll eccentricity constantly changes asthe rolls wear and they are replaced with reground rolls, or as a resultof bearing and lubrication variations.

Present demands by the industry require a rolling mill control system toprovide greater gage control accuracy and increased production levels.In order to meet these demands, such a control must compensate for theeffects of roll eccentricity during operation of the rolling mill.Present-day requirements further demand a large degree of versatility inthe control system in order to economically utilize the productioncapacity of a given rolling mill installation. In a cold rolling millinstallation, for example, it is desirable to establish a rollingschedule which oftentimes requires different modes of operation for oneof more mill stands to process the coils of strip. Certain coils ofstrip are rolled with the objective of producing uniform gage, thusrequiring repeated roll gap adjustments to suit the varying rollingconditions in the mill; while other coils of strip are rolled with theobjective of temper or skin pass rolling to improve their metallurgicalproperties, thus requiring the use of uniform rolling force throughoutthe rolling operation.

Recent attempts to improve the gage accuracy of rolled strip include theuse of hydraulic roll force actuators in the form of piston and cylinderassemblies for adjusting the gap between the processing rolls duringrolling. Tests have now established that these actuators are capable ofmaking roll gap changes in response to signals having a frequency ashigh as 20 cycles per second with no appreciable attenuation. It is afeature of the present invention to control these actuators in a mannerto meet the present requirements of the industry.

SUMMARY OF THE INVENTION In accordance with the invention, an improvedautomatic gage control system for a rolling mill is provided includingcontrol circuitry to compensate for the effects of roll eccentricityduring operation of the rolling mill and to simulate a rolling millstructure having variable stretch characteristics.

Specifically, the present invention provides a control system forhydraulic roll force actuators in a rolling mill to respond to theeffects of roll eccentricity and compensate for them by actuatoradjustments of an exact amount to prevent a rolling force increase. Theactuators are controlled in response to deviations in the rolling forceto compensate for the effects of roll eccentricity and/or simulate amill structure with variable The rolling force signal P is received bycircuitry to produce a signal A P representing a change in the rollingforce. Thus, with a given change in the rolling force, there is computeda change in the housing stretch A h given by the equation:

A h AP/M To simulate an infinitely stiff mill, the control systemoperates on the basis to control the displacement of the forceapplicator by an amount to exactly correspond to the change in thehousing stretch. If the hydraulic actuator is controlled to move by thesame amount but in an opposite direction thereby rejecting anyincremental changes in the rolling force, the resultant controlsimulates a mill structure having an infinitely soft stretchcharacteristic. By selecting the midpoint between these two extremes ofstretch characteristics, the control system will simulate the millstretch characteristic of a conventional rolling mill. By simulating aninfinitely soft rolling mill, it was found that any increase in the rollforce can be rapidly prevented. This would include roll force increasesproduced by roll eccentricity and thus they can be completely eliminatedby such a control system. Since this control system operates to rejectall roll force increases, an outer gage control loop or tension controlloop are concurrently employed to provide automatic gage control.

These features and advantages of the present invention as well as otherswill become more apparent when the following description is read inlight of the accompanying drawings, of which:

FIG. 1 is a schematic block diagram of electrical circuitry forcontrolling a rolling mill in accordance with the teachings of thepresent invention; and

FIG. 2 is a detailed schematic circuit diagram of the rolling millcontrol system according to the present invention.

With reference now to the drawings, and particularly to FIG. 1, therolling mill shown includes a housing 10 having windows which rotatablysupport upper and lower back-up rolls 11 and 12, respectively. Eachbackup roll supports a work roll 13 which forms a roll gap wherein astrip S is processed. After leaving the gap between the work rolls, thestrip passes beneath an X-ray 14 from where it partially wraps about theouter surface of a deflector roll 15 and then continues in the downwarddirection to a point where it is formed into a coil 16 by a mandrel 17.At the top of the mill housing 10, there is provided a screwdown whichincludes a screw 18 for establishing a desired gap between the workrolls. Between the screw and the roll chocks for the back-up roll 11,there is arranged a load cell 19 for providing a signal in line 21proportional to the total roll force P in the mill.

At the bottom of the mill housing between the roll chocks of the lowerback-up roll 12 and the housing,

there is provided a roll force actuator 22 in the form of a piston 23and cylinder 24. Hydraulic fluid is delivered from a source, not shownin the drawings, to a servo valve 25 employed to control the passage offluid through pipes 27 to the actuator 22. A position sensor 28 such asan LVDT delivers an electrical signal in line 29 proportional to therelative position of the piston 23 with respect to the cylinder 24. Therolling force signal P is delivered to a housing stretch modulator 31having electrical circuitry, to be more fully described hereinafter,which provides a signal in line 32 proportional to the elongation orstretch of the mill housing in response to a change in the rollingforce. This signal which is given by the equation:

- A h AP/M has a negative electrical polarity and is connected to oneside of a potentiometer or rheostat 33. The output signal from thehousing stretch modulator 31 is also connected by line 34 to aproportional plus derivative circuitry 35. The circuitry 35 produces asignal representing the same degree of mill housing stretch but having apositive electrical polarity and proportional to the quantity given bythe equation:

+ A h +AP/M Line 36 is connected to the contact of potentiometer 33 atits adjustment extreme opposite from the contact point of line 32. Thepotentiometers 33 includes a movable tap 37 constructed for manualpositioning by an operator. Depending on the position of the movabletap, a signal lying between or equal to one of the quantities and + AP/Mis delivered by line 38 to an actuator position controller 39. Theposition sensor signal in line 29 is used as a feedback signal by thecontroller 39 to generate an actuator position control signal in line 40connected to a servo valve current controller 41 which also receives afeedback signal in line 42 from the servo valve 25. A positionadjustment signal for the actuator 22 is transmitted by line 43 to theservo valve 25 for accurate and rapid roll gap changes by the actuator.As previously indicated, these actuators are responsive to signalshaving a frequency as high as cycles per second with no appreciableattenuation.

When an operator positions the movable tap 37 to receive the signalproportional to the quantity in line 36, the rolling mill control systemsimulates an infinitely rigid mill construction whereby the roll gapadjustment made by the roll force actuators 22 is an the control systemfunctions on the basis of simulating a rolling mill having infinitelysoft mill stretch characteristic whereby the increase in the housingstretch is immediately responded to by the cylinder position controller39 in a manner to reject the increase and maintain the rolling forceconstant. By simulating an infinitely soft rolling mill housingstructure, the control system compensates for the effects of rolleccentricity by maintaining a constant rolling force and rejecting anyincreases to the rolling force. When an infinitely soft mill issimulated, temper rolling or skin pass rolling may be effected whereby atruly constant rolling force is provided at the roll gap.

An outer gage control loop is added when the control system is employedto compensate for the effects of roll eccentricity while processingstrip to a uniform thickness. Such a gage control loop includes, forexample, the X-ray 14 whose strip thickness deviation signal istransmitted along line 51 to a gage control amplifier 52 whose outputsignal is transmitted by line 53 to a switch 54. The switch 54 receivesfrom line 55 an error signal from a tension controller 56 associatedwith the deflector roll 15 in a manner to provide uniform tension in thestrip at the delivery side of the mill. When the switch 54 is actuated,an automatic gage control signal is produced in line 57 representingeither the X-ray gage control signal from line 53 or the tension controlsignal from line 55. Alternatively, the switch may feed either both ornone of these two signals to line 57. When both signals are transmitted,the gage control function is divided between tension and roll gapadjustments.

Turning now to the schematic circuit diagram of the present inventionillustrated in FIG. 2, the load cell 19 provides a signal in line 21proportional to the rolling force P between the work rolls. The rollingforce signal passes through resistor 60 to a summing point 61. Point 61is connected by a line 62 through resistor 63 to a potentiometer 64manually set to a desired rolling force reference signal P Point 61 mayalso receive an automatic gage control signal in an outer control loopfrom line 65 connected through a resistor 66 to a switch 67. This switchis designed to transmit either, both or neither of two input signalsconsisting of a tension control error signal in line 68 and a thicknesserror signal in line 69.

The thickness error circuitry includes a tension reference signalprovided by potentiometer 70 in line 71 passing through a resistor 72 toa summing point 73. Point 73 is connected through a resistor 74 to atensiometer 75. The tensiometer 75 when incorporated as part of thedeflector roll apparatus 15 produces a signal proportional to the actualstrip tension at the delivery side of the mill. Point 73 is alsoconnected to the input of an integrating operational amplifier 76 havinga feedback path including resistor 77 in series with capacitor 78. Theoutput signal from amplifier 76 is transmitted by line 68 to switch 67.

The circuitry for producing the gage error signal includes an actualstrip thickness signal from X-ray gage 14 in line 51 through resistor 79to a summing point 80. The point 80 is connected by line 81 through aresistor 82 to a potentiometer 83, manually set to represent a desiredstrip thickness reference signal. Point 80 is also connected to theinput of a proportional operational amplifier 84 having a feedback pathincluding resistor 85. The output signal from amplifier 85 istransmitted by line 69 to switch 67. Returning now to point 61, it isconnected to the input of a proportional operational amplifier 90 havinga feedback path including a resistor 91. The resistor 91 has aresistance proportional to the known mill modulus M,,, and representsthe quantity.

The signal from amplifier 90 in line 93 is connected to one side of amanually set potentiometer 92 and is proportional to a change in thehousing stretch given by the quantity The output signal from amplifier90 in line 93 is applied through a resistor 94 to a proportionaloperational amplifier 95 having a feedback path including a resistor 96.The output from amplifier 96 is a signal in line 97 connected to theopposed contact point of potentiometer 92 and represents the quantityAP/M The signal in line 97 is produced as an inverted signal such thatquantitatively, it is equal to but having an electrical polarityopposite to the signal in line 93. The potentiometer 92 includes amovable tap 98 for transmitting to line 99 the signal in line 93, line97 or proportional parts of the signal quantities lying between theranges of these signals. Line 99 is connected through resistor 101 to asumming point 102. Point 102 is connected through resistor 103 to line29 of the position sensor 28 of the roll force actuator 22. Point 102 isalso connected to the input of a proportional operational amplifier 104having a feedback path including a resistor 105. The amlifier 104 isemployed as an actuator position controller having an output signaltransmitted by line 106 through a resistor 107 to a summing point 108.Point 108 receives a feedback signal in line 109 through resistor 110 inline 42 from the servo valve 25. Line 42 is connected to ground througha resistor 111. Point 108 is also connected to the input of anoperational amplifier 112 having a feedback path including a resistor113. The amplifier 112 is employed as a servo valve current controller.As previously indicated, the servo valve controls the passage of fluidpressure to the hydraulic force actuator in the pipes 27.

Let is be assumed that an operator elects to employ the control systemaccording to the present invention to simulate an infinitely stiff millin which event he will position the movable tap 98 of the potentiometer92 to receive the signal proportional to the quantity in line 97. As theprocessing of the strip takes place, the load cell 19 at the top of themill housing continually senses the rolling load P. Let is be assumedthat a gage error occurs for any one of a number of well-known reasonsin which event the load cell reading will deviate from the rolling loadreference P.,. This deviation is computed by the control circuit toprovide a housing stretch change signal Ah AP/M in line 99 which is thenfed to the position controller amplifier 104. Should there at the sametime occur a relative displacement between the piston and the cylin- LIIder of the roll force applicator, then this actuator position change isrepresented by a position feedback signal in line 29 to the cylinderposition controller amplifier 104. The amplifier 104 provides an errorsignalin line 106 for servo valve current controller amplifier 112 toadjust the servo valve to position the hydraulic actuator to reduce theerror to zero.

Let is now be assumed that the operator selects a mode of rolling millcontrol to simulate an infinitely soft rolling mill in which event hewill position the movable tap 98 to receive the signal AP/M in line 93.As rolling proceeds, should the rolling force P increases, for example,due to an increase in the incoming strip thickness or the eccentricitycharacteristic of the rolls, the electrical signal in line 28 representsa housing stretch change computed by the equation:

A h AP/M This signal is fed to the cylinder position controlleramplifier 104 where it is also combined with the position feedbacksignal from the cylinder position sensor as previously indicated. Thecontroller then provides an output signal for the servo valve currentcontroller to adjust the servo valve in a manner that will cause thepiston to be immediately retracted within the cylinder by an amountequal to to restore the roll force to its original value and therebymaintain a constant rolling force and eliminate the detrimental effectsof roll eccentricity. When the control system simulates an infinitelysoft mill modulus, gage corrections are prevented. In the event the millstand is to provide automatic control gage, the outer gage control loopis added by switch 67 to modify the roll force reference signal P Thisouter gage control loop may be provided by tension controller errorsignal, the thickness error signal, or a combination of the signals fromlines 68 and 69 as determined the manuallypositioned switch 67.

Although the invention has been shown in connection with certainspecific embodiments, it will be read ily apparent to those skilled inthe art that various changes in form and arrangement of parts may bemade to suit requirements without departing from the spirit and scope ofthe invention.

I claim as my invention:

1. A method of controlling the gap between processing rolls of a rollingmill to simulate a rolling mill structure selected to have a stretchcharacteristic within a range of infinitely stiff and infinitely softduring operation of rolling mill, said rolling mill including a housingfor resisting the rolling force produced between said processing rollsand hydraulic force actuators carried in said housing for adjusting saidroll gap, said method of controlling comprising the steps of:

generating a first signal representing a change in the roll gapproportional to a first change in the stretch of said rolling millstructure;

generating a second signal to represent a change in the roll gapproportional to a second change in the housing stretch in a directionopposite to said first change;

selecting a roll gap position control signal within a range defined bysaid first and second signals; and

controlling said hydraulic roll force actuator in such a way to reducethe said roll gap position control signal to zero.

2. The method of claim 1 including the steps of:

generating an initial electrical signal proportional to said rollingforce developed between said processing rolls; and

modifying said initial electrical signal in accordance with the equationto generate said first electrical signal, where h equals the actual rollgap, P equals rolling force, and M equals modulus of said rolling millstructure.

3. The method of claim 2 including the steps of:

generating a position feedback signal from said roll force actuator; and

modifying said roll position control signal with said position feedbacksignal.

4. The method of claim 3 including the steps of:

generating a gage control error signal; and

modifying said second signal with said gage control error signal.

5. The method of claim 3 including the steps of:

generating a tension controller error signal; and

modifying said second signal with said tension controller error signal.6. The method of claim 1 wherein said roll gap position control signalproduces a frequency of response by said hydraulic roll force actuatorof up to 20 cycles per second.

7. A method for controlling a rolling mill wherein eccentriccharacteristics of the rolls rotating in the mill produce cyclic changesin the rolling force developed between the processing rolls, saidrolling mill including a housing for resisting the rolling forceproduced between said processing rolls and hydraulic roll forceactuators carried by said housing for adjusting the gap between saidprocessing rolls, said method comprising the steps of:

computing a change in the housing stretch as a function of a change inthe rolling force due to said eccentricity characteristics of the rolls;and

controlling said hydraulic roll force actuator in such a way tocompensate for a change in the said housing stretch by preventingrolling force increases between said processing rolls due to saideccentricity characteristics.

8. The method of claim 7 including the steps of:

generating a first electrical signal proportional to said rolling force;and

modifying said first electrical signal in accordance with the equationfor computing an actual change in the housing stretch, where h equalsthe actual roll gap, P equals rolling force, and M equals modulus of themill housing. 9. The method of claim 8 including the steps of:generating a second electrical signal proportional to said change in therolling force; generating a gage control error signal; and modifying sidelectrical signal by the combination with said gage control errorsignal. 10. The method of claim 8 including the steps of:

generating a second electrical signal proportional to said change in therolling load; generating a tension control error signal; and modifyingsaid second electrical signal by the combination with said tensioncontrol error signal.

11. The method of claim 7 including the step of producing an errorsignal having a response time by said actuator of up to cycles persecond for said step of controlling said hydraulic roll force actuator.

12. A control system for a rolling mill of the type employed to simulatea stretch characteristic of the rolling mill structure selected from arange of stretch characteristics between infinitely stiff and infinitelysoft under the rolling forces developed between the processing rollsduring the rolling of strip-like material comprising:

means for generating a first signal proportional to the rolling forcedeveloped between said processing rolls;

means receiving said first signal for generating a second signalproportional to a change in the housing stretch due to a change in saidrolling force;

means receiving said second signal for generating a third signalrepresenting an inverted housing stretch signal having an electricalpolarity opposite to said second signal;

control signal selection means receiving said second and third signalsfor delivering a roll gap adjusting signal selected to simulate arolling mill structure having a desired stretch characteristic; and

means inlcuding a fluid actuator for adjusting said gap formed betweensaid processing rolls in response to said roll gap adjusting signal. 13.A control system according to claim 12 wherein said control signalselection means including a potentiometer having a movable tap, saidpotentiometer having a first input contact receiving said second signal,said potentiometer further including a second input contact electricallyopposed to said first input contact and receiving said third electricalsignal.

14. A control system for a rolling mill of the type employed tocompensate for eccentricity characteristics of rolls while rotating in amill which produce cyclic changes in the gap defined by the processingrolls, said rolling mill including housing means for rotatablysupporting said rolls, fluid actuated means carried by said housingmeans for adjusting said roll gap defined by the processing rolls, theimprovement comprising:

means for generating a signal proportional to elastic changes of thehousing means as a function of said eccentricity characteristics of therolls in the mill;

a control circuit receiving said signal for generating a rolleccentricity compensating signal proportional to a roll gap change foreliminating said elastic changes; and

control means receiving said roll eccentricity compensating signal foradjusting said fluid actuated means.

15. A control system according to claim 14, the improvement furthercomprising:

gage error signal generating means for modifying said signalproportional to elastic changes of the housing means.

16. A control system according to claim 14, the improvement furthercomprising:

means for generating a tension control error signal to modify saidsignal proportional to elastic changes of the housing means.

1. A method of controlling the gap between processing rolls of a rollIngmill to simulate a rolling mill structure selected to have a stretchcharacteristic within a range of infinitely stiff and infinitely softduring operation of rolling mill, said rolling mill including a housingfor resisting the rolling force produced between said processing rollsand hydraulic force actuators carried in said housing for adjusting saidroll gap, said method of controlling comprising the steps of: generatinga first signal representing a change in the roll gap proportional to afirst change in the stretch of said rolling mill structure; generating asecond signal to represent a change in the roll gap proportional to asecond change in the housing stretch in a direction opposite to saidfirst change; selecting a roll gap position control signal within arange defined by said first and second signals; and controlling saidhydraulic roll force actuator in such a way to reduce the said roll gapposition control signal to zero.
 2. The method of claim 1 including thesteps of: generating an initial electrical signal proportional to saidrolling force developed between said processing rolls; and modifyingsaid initial electrical signal in accordance with the equation h P/Mm togenerate said first electrical signal, where h equals the actual rollgap, P equals rolling force, and Mm equals modulus of said rolling millstructure.
 3. The method of claim 2 including the steps of: generating aposition feedback signal from said roll force actuator; and modifyingsaid roll position control signal with said position feedback signal. 4.The method of claim 3 including the steps of: generating a gage controlerror signal; and modifying said second signal with said gage controlerror signal.
 5. The method of claim 3 including the steps of:generating a tension controller error signal; and modifying said secondsignal with said tension controller error signal.
 6. The method of claim1 wherein said roll gap position control signal produces a frequency ofresponse by said hydraulic roll force actuator of up to 20 cycles persecond.
 7. A method for controlling a rolling mill wherein eccentriccharacteristics of the rolls rotating in the mill produce cyclic changesin the rolling force developed between the processing rolls, saidrolling mill including a housing for resisting the rolling forceproduced between said processing rolls and hydraulic roll forceactuators carried by said housing for adjusting the gap between saidprocessing rolls, said method comprising the steps of: computing achange in the housing stretch as a function of a change in the rollingforce due to said eccentricity characteristics of the rolls; andcontrolling said hydraulic roll force actuator in such a way tocompensate for a change in the said housing stretch by preventingrolling force increases between said processing rolls due to saideccentricity characteristics.
 8. The method of claim 7 including thesteps of: generating a first electrical signal proportional to saidrolling force; and modifying said first electrical signal in accordancewith the equation h P/Mm for computing an actual change in the housingstretch, where h equals the actual roll gap, P equals rolling force, andMm equals modulus of the mill housing.
 9. The method of claim 8including the steps of: generating a second electrical signalproportional to said change in the rolling force; generating a gagecontrol error signal; and modifying sid electrical signal by thecombination with said gage control error signal.
 10. The method of claim8 including the steps of: generating a second electrical signalproportional to said change in the rolling load; generating a tensioncontrol error signal; and modifying said second electrical signal by thecombination with said tension control error signal.
 11. The method ofclaim 7 including the step of producing an error signal having aresponse time by said actuator of up to 20 cycles per second for saidstep of controlling said hydraulic roll force actuator.
 12. A controlsystem for a rolling mill of the type employed to simulate a stretchcharacteristic of the rolling mill structure selected from a range ofstretch characteristics between infinitely stiff and infinitely softunder the rolling forces developed between the processing rolls duringthe rolling of strip-like material comprising: means for generating afirst signal proportional to the rolling force developed between saidprocessing rolls; means receiving said first signal for generating asecond signal proportional to a change in the housing stretch due to achange in said rolling force; means receiving said second signal forgenerating a third signal representing an inverted housing stretchsignal having an electrical polarity opposite to said second signal;control signal selection means receiving said second and third signalsfor delivering a roll gap adjusting signal selected to simulate arolling mill structure having a desired stretch characteristic; andmeans inlcuding a fluid actuator for adjusting said gap formed betweensaid processing rolls in response to said roll gap adjusting signal. 13.A control system according to claim 12 wherein said control signalselection means including a potentiometer having a movable tap, saidpotentiometer having a first input contact receiving said second signal,said potentiometer further including a second input contact electricallyopposed to said first input contact and receiving said third electricalsignal.
 14. A control system for a rolling mill of the type employed tocompensate for eccentricity characteristics of rolls while rotating in amill which produce cyclic changes in the gap defined by the processingrolls, said rolling mill including housing means for rotatablysupporting said rolls, fluid actuated means carried by said housingmeans for adjusting said roll gap defined by the processing rolls, theimprovement comprising: means for generating a signal proportional toelastic changes of the housing means as a function of said eccentricitycharacteristics of the rolls in the mill; a control circuit receivingsaid signal for generating a roll eccentricity compensating signalproportional to a roll gap change for eliminating said elastic changes;and control means receiving said roll eccentricity compensating signalfor adjusting said fluid actuated means.
 15. A control system accordingto claim 14, the improvement further comprising: gage error signalgenerating means for modifying said signal proportional to elasticchanges of the housing means.
 16. A control system according to claim14, the improvement further comprising: means for generating a tensioncontrol error signal to modify said signal proportional to elasticchanges of the housing means.